Nope. It's 160 acres.
1 sq mi = 5280ft x 5280ft = 27,878,400 sq. ft.
1 ac = 43,560 sq. ft.
27,878,400 : 43,560 = 640 acres
640 : 4 = 160
Well, I guess it depends on how they marked off the 1/4 square mile. I live on a piece that is 1/4 mile on a side...that is 40 acres. So I guess 40 acres is 1/4 mile squared and 160 acres is 1/4 squared miles. I think your interpretation is correct for the way it's used in this article.